This description relates to a composite nozzle assembly, and, more particularly, to a method and system for interfacing a ceramic matrix composite component to a metallic component in a gas turbine engine.
At least some known gas turbine engines include a core having a high pressure compressor, combustor, and high pressure turbine (HPT) in serial flow relationship. The core engine is operable to generate a primary gas flow. The high pressure turbine includes annular arrays (“rows”) of stationary vanes or nozzles that direct the gases exiting the combustor into rotating blades or buckets. Collectively one row of nozzles and one row of blades make up a “stage”. Typically two or more stages are used in serial flow relationship. These components operate in an extremely high temperature environment, and may be cooled by air flow to ensure adequate service life.
HPT nozzles are often configured as an array of airfoil-shaped vanes extending between annular inner and outer bands which define the primary flowpath through the nozzle. Due to operating temperatures within the gas turbine engine, materials having a low coefficient of thermal expansion are used. For example, to operate effectively in such adverse temperature and pressure conditions, ceramic matrix composite (CMC) materials may be used. These low coefficient of thermal expansion materials have higher temperature capability than similar metallic parts, so that, when operating at the higher operating temperatures, the engine is able to operate at a higher engine efficiency. However, such ceramic matrix composite (CMC) have mechanical properties that must be considered during the design and application of the CMC. CMC materials have relatively low tensile ductility or low strain to failure when compared to metallic materials. Also, CMC materials have a coefficient of thermal expansion which differs significantly from metal alloys used as restraining supports or hangers for CMC type materials. Therefore, if a CMC component is restrained and cooled on one surface during operation, stress concentrations can develop leading to a shortened life of the segment.
To date nozzles formed of CMC materials have experienced localized stresses that have exceeded the capabilities of the CMC material, leading to a shortened life of the nozzle. The stresses have been found to be due to moment stresses imparted to the nozzle and associated attachment features, differential thermal growth between parts of differing material types, and loading in concentrated paths at the interface between the nozzle and the associated attachment features.